1. Department of Computer Science & Engineering, University of Washington, Seattle, WA 98195-2350, USA
2. Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven CT 06520-8103, USA
3. Department of Molecular, Cellular and Developmental Biology, Department of Molecular Biophysics and Biochemistry, and Howard Hughs Medical Institute, Yale University, New Haven, CT 06520-8103, USA
4. Department of Computer Science & Engineering, and, Department of Genome Sciences, University of Washington, Seattle, WA 98195-2350, USA